Electromagnetic waves may be transferred from place to place through a conductor. In wired transmission, the conductor is usually a wire or other solid substance. In wireless transmission, the conductor is usually an ambient substance, such as air, water, etc. A transmitter typically converts electrical energy into a signal, which is then broadcast via carrier wave through an antenna to a receiver's antenna. Repeaters, middle stations, etc. may be used as intermediates in the transmission to sustain the integrity of the transmitted wave.
The electrical energy input into a transmitter usually results from some intelligence being generated by a sender, such as voice, data, etc. Various digital signal processing techniques are then applied to the information content to provide spectrally efficient transmission. The signal processing techniques can result in signals that have a constant or non-constant envelope characteristic. Constant envelope signals typically use a non-linear transmit line-up while a more linear transmit line-up is typically required for non-constant envelope signals. This signal is then modulated onto a carrier wave by the transmitter. The now modulated carrier wave is the transmitted electromagnetic signal. A receiver may then demodulate the signal, by deconstructing the modulated carrier wave into a copy of the initial intelligence sent by the transmitter.
Various techniques are used to modulate the carrier wave. For example, carrier waves in wireless transmission may be modulated on to signals by varying wave characteristics, such as amplitude, frequency and phase. Modulation may occur through linear or non-linear techniques. Linear techniques typically modulate frequency and/or phase and amplitude characteristics of a non-constant envelope signal. Non-linear techniques typically modulate frequency and/or phase characteristics of a constant envelope signal.
In some areas of signal processing, however, such as radio frequency (RF), linear techniques lead to less than desirable results. For example, linear techniques usually involve linear amplifiers, which can offer relatively precise modulation and therefore transmission. However, the power draw required by linear amplifiers limits their usefulness, especially in portable, battery driven devices.
Attempts have been made in the art to overcome these difficulties. For example, amplifier combining—using multiple amplifiers to amplify the same signal—is one method that attempts to leverage linear and non-linear benefits. However such attempts to date have been constrained by various difficulties. For example, amplifier combining methods use components, such as transformers or quarter wave lines, to sum the output of the amplifiers in order to drive the load. These components add to the cost and size of the amplifier array.
Transmitters may need to support a combination of constant and non-constant envelope pulse processing schemes such as when a transmitter is used for multiple modes of operation (e.g., GSM and EDGE). The need to support multiple pulse processing schemes has led to costly and inefficient architectures. Traditionally, multiple modulation schemes in a single transmitter have been provided through either: single modulation architectures, which provide less than optimal solutions; or, multiple modulation architectures, which increase cost and complexity of the transmitter.
Accordingly, it would be helpful to the art of electromagnetic transmission if non-linear amplification techniques could be used in combination with linear amplification techniques.
It would be further helpful if systems, methods and articles of manufacture could be provided that facilitate multiple modulation schemes in a single transmitter.